Modern telephony networks, particularly mobile networks, are increasingly implemented as so-called intelligent networks (IN). Such networks have increased functionality compared with conventional networks and permit a real-time or near real-time query and response process which enables the network to apply enhanced routing information to call termination (connection) processes. An example of such an application is in telephony billing procedures applied by most telephony networks, most notably in the case of networks which allow users/subscribers to make use of prepaid airtime. In the case of a mobile network, a call made by a subscriber is processed by the intelligent network to determine near-instantaneously whether or not the subscriber has sufficient airtime to make a requested call. In the case of conventional networks, an intelligent network may determine whether or not a caller utilising a public telephone has inserted a prepaid smart card with sufficient credit thereon to make a call.

The above is but one example of the functionality available in intelligent networks.

It is an object of the invention to provide a method and system which exploits the functionality of an intelligent telephony network.

SUMMARY OF THE INVENTION According to the invention there is provided a method of operating a telephony network, the method comprising: receiving a call request from a telephone of a caller and routing the call request to a telephone of a called recipient; receiving a response signal from the telephone of the called recipient in response to the call request, the response signal indicating the call recipient's willingness to accept a reverse-charge or shared-charge call ; processing the response signal from the call recipient to initiate billing of the call recipient, and routing a corresponding modified call request to the call recipient; and on acceptance of the modified call request by the call recipient, connecting the call, so that at least a portion of the cost associated with the call is allocated to the call recipient.

The call request may comprise a sequence of dialed digits corresponding to the telephone number of the call recipient.

Preferably, the sequence of dialed digits corresponds exactly to the telephone number of the call recipient.

Alternatively, the call request may comprise a sequence of dialed digits corresponding to the telephone number of the call recipient and a prefix and/or suffix comprising a predetermined sequence of dialed digits and/or symbols indicating that the caller wishes to set up a reverse-charge or shared-charge call. The response signal from the call recipient may be sent by pressing a predetermined button or buttons on a mobile telephone of the call recipient.

Preferably, the predetermined button is the red"cancel"button on said mobile telephone.

Alternatively, the predetermined buttons may be the"star"and green"send" buttons on said mobile telephone, wherein the"star"and"send"buttons are pressed simultaneously or wherein the"star"button is pressed, followed by the"send"button.

In the preferred embodiment of the method, the response signal is interpreted by the network as a busy divert signal to a predetermined telephone number.

Preferably, the predetermined telephone number is the call recipient's own telephone number.

In an alternative embodiment of the invention, the response signal from the call recipient is sent by raising and lowering the receiver on a conventional telephone of the call recipient.

The method may include vetting the status of the call recipient to determine whether or not the call recipient has sufficient credit or prepaid airtime to pay the costs associated with the presented call.

The modified call request may be indicated to the caller and/or the call recipient as an alternative ringing tone, to alert the caller and/or call recipient to the fact that the call recipient has provisionally accepted the call on a reverse-charge or shared-charge basis.

Having provisionally indicated willingness to accept a reverse-charge or shared-charge call, the call recipient may accept the modified call request directly, divert the call, or choose not to answer the call by allowing it to ring.

The network may allocate all of the costs associated with an accepted call to the call recipient.

Alternatively, the network may allocate a portion of the costs associated with the call to the call recipient and a portion to the caller.

In one version of the invention, the caller may be identified as belonging to a group of approved callers to whom a predetermined cost sharing scheme applies.

BRIEF DESCRIPTION OF THE DRAWINGS The single drawing is a highly simplified schematic diagram of a mobile network infrastructure suitable for implementing the method of the invention.

DESCRIPTION OF EMBODIMENTS Figure 1 shows, in a highly simplified schematic form, a portion of the architecture of a modern GSM mobile telephone network. The diagram does not purport to be comprehensive but merely illustrative. The network will typically embody intelligent network (IN) functionality, but this is not essential for implementation of the invention.

In Figure 1, a mobile telephone 10 of a caller communicates with a first base station 12 which in turn communicates with a mobile switching center (MSC) 14. Associated with the mobile switching center 14 is a visitor location register (VLR) 16.

A call recipient has a mobile telephone 18 which communicates with a second base station 20. The base station 20 is connected to a gateway mobile switching center (GMSC) 22 with its own associated visitor location register 24. The respective mobile switching centers 14 and 22 and the respective visitor location registers 16 and 24 are interconnected as shown.

The visitor location registers are also connected to a home location register (HLR) database 26 and to a billing center 28. The GMSC 22 is also connected to the billing center. The HLR is a central database containing data relating to the account status, prepaid credit balance (if applicable) and predetermined network settings of subscribers such as call settings, in particular call divert and call waiting settings. The VLRs are decentralised databases which are updated with data from the HLR relating to a particular subscriber when that subscriber's telephone connects to the MSC in question.

In normal telephony sequencing, a ca) ier diats a sequence of digits representing the telephone number of a call recipient. In the case of a caller using a mobile telephone, the telephone buttons corresponding to the required digits are pressed and the green"connect"button is pressed to connect the call. In the case of a caller utilising a conventional telephone on a fixed line network, the user lifts the receiver off hook and then dials the required digits. In either case, the network connects (terminates) the call and rings the telephone of the call recipient.

In a modern mobile network such as that illustrated schematically in Figure 1, subscriber data is stored in the home location register 26 and a subscriber's data is propagated from the home location register to the applicable visitor location register when the subscriber's mobile telephone connects to the network via the respective base station system and mobile switching center. As mentioned above, the register describes various attributes applicable to the subscriber, such as the status of the subscriber's account, as well as call settings, in particular call divert and call waiting settings. In particular, the call divert setting referred to as the "busy divert"is important in the context of the present invention. Conventionally, a busy divert is implemented automatically when a call recipient receives a new call request while engaged on an active call, and/or manually by the call recipient by the sending of a"busy"command.

Such a command is sent by pressing the red"cancel"button on the mobile telephone, either while engaged on an active call in response to an incoming call, or simply in response to such an incoming call even when not engaged.

The invention proposes to utilise this existing functionality to provide enhanced flexibility in implementing call and billing management including reverse-charge and shared-charge calling.

In the case of a conventional fixed-line network, the equivalent of pressing the red"cancel"button on a mobile telephone can be achieved by rapid lifting and replacing of the receiver in response to a new call.

An embodiment of the method will now be described in greater detail.

When the caller 10 dials the call recipient's number, this is interpreted as a call request by the mobile switching center 14, which determines from the visitor location register 16 the account status of the caller. The call request is routed to the mobile switching center 22 and thence via the base station 20 to the call recipient 18. In a preferred embodiment of the invention, the call request comprises a sequence of dialed digits that corresponds exactly to the call recipient's telephone number, but could in other embodiments include a prefix and/or suffix, such as a predetermined sequence of dialed digits and/or symbols, to indicate to the network that the caller wishes to set up a reverse-charge or shared-charge call.

If the call recipient is prepared to accept a reverse-charge or shared-charge call from the caller, he/she presses the red"cancel"button (or lifts and replaces the receiver in quick succession on a conventional telephone).

This action, conventionally interpreted by the network as a"busy divert", is interpreted by the network as a response signal from the call recipient. It is proposed that subscribers making use of the invention set their"divert on busy"settings to divert calls to their own number. On receiving the response signal from the call recipient, the mobile switching center 22 performs credit vetting and any other processes required to determine whether or not the call recipient has sufficient credit or prepaid airtime to pay the costs associated with the presented call. (This process assumes a typical or average call cost. ) If the call recipient has customised his/her user profile, any relevant settings can be applied.

For example, if a subscriber does not wish to make use of the functionality of the present invention, the subscriber's"divert on busy"setting can simply be set to any number other than the subscriber's own number, which effectively disables the reverse-charge calling system.

Other processes such as security processes can be applied at this stage.

For example, the call recipient may be requested to enter an authorisation code or personal identification number to authorise the reverse or shared- charge call process. Such a feature may be particularly useful in the case of a telephone which is used by more than one person.

Having received the special"divert on busy"response signal from the call recipient and having established that credit or airtime is available to pay for the call, the mobile switching center 22 now treats the call as originating from the call recipient by simply transposing the calling (a) and called (b) numbers. The mobile switching center 22 now loops the call back to the call recipient, presenting it for the second time. At this point, an alternate ringing tone is preferably presented to the caller and/or call recipient, indicating that the call has been accepted as a reverse-charge or shared- charge call. The above described processes are carried out near- instantaneously.

The call recipient now has several options. Firstly, the call recipient can accept the call by pressing the green button on his/her mobile phone or lifting the receiver on a conventional telephone to accept the call. The call then is conducted normally, except that the call recipient is billed at least partially for the cost of the call.

Secondly, the call recipient can divert the call by pressing the red"cancel" button on a mobile telephone or by lifting and replacing the receiver in quick succession on a conventional telephone. This divert signal is interpreted by the mobile switching center 22 as an instruction to divert the call to the call recipient's voicemail service at the expense of the call recipient.

A third option available to the call recipient is to simply allow the telephone to ring. Having previously indicated willingness to accept a reverse-charge or shared-charge call, if the call recipient now simply allows the telephone to ring without answering, this can indicate to the caller (via the changed ringing tone) that the call recipient is busy and will return the call in due course. Any normal diverts which have been set by the call recipient can be applied.

As an alternative to using the red"cancel"button to send a busy divert signal, the call recipient could instead press the green"send"button to accept the call, and simultaneously or in quick succession press a further designated button such as the star (*) key to indicate to the network that the call is being accepted as a reverse-charge or shared-charge call. The sequence could be"send", "star"or vice versa in the case where the keys are not pressed simultaneously. The advantage of pressing the"star" button first is that this effectively qualifies the pressing of the"send"button, avoiding the risk of initiating conventional billing of the caller.

In variations of the above described basic embodiment, the cost of the call can be shared between the caller and the call recipient equally or in predetermined unequal proportions. For example, if the caller belongs to a predefined shared call group set up by the call recipient, and the above described method is followed, the network distributes the cost of the call equally between the caller and the call recipient in what can be described as a partnership call or business call scheme.

In a further variation, the caller may be a member of a discounted caller group (for example, family and friends of the call recipient). When the sequence described above is initiated the network distributes the cost of the call unequally between the caller and the call recipient so that the call recipient assumes a portion of the call cost, in effect discounting the cost of the call to the caller.

A further variation of the method of invention may be applied in countries such as the USA and Canada where a different model of call charging is used compared with most other countries. In these countries, the caller and call recipient generally both contribute to the cost of the call equally, if the caller and the call recipient are on the same network, or in different proportions when the caller and the call recipient are on different networks.

In such a case, the mobile switching center 22 performs a somewhat more complex billing algorithm in terms of which the call recipient assumes both the called and calling cost, either completely or in a greater proportion than normal.

It will be appreciated that the present invention can be applied to various types of networks, including fixed, mobile and satellite networks and the Internet. The caller and the call recipient may be subscribers of the same network or different networks, meaning that a caller using any form of telephone can originate a call, allowing the call recipient to selectively accept such a call while it is ringing on a reverse-charge or shared-charge basis.

The method of the present invention can be implemented without any substantial changes to the conventional architecture of the above described network (or other networks), and the necessary functionality can readily be programmed into the relevant network components. An advantage of the present invention, compared with alternative proposals for reverse-charge billing and related functionality in an intelligent network, is that once the network has been programmed and configured appropriately, no additional setup is required on a subscriber by subscriber basis in order to use the new functionality provided. Thus, the invention represents what is known as"zero administered technology"whereby users of the service are enabled without having to set up or configure the service individually. Of course, it is possible to cater for the possibility of individual subscribers wishing to limit or cancel the enhanced functionality.

A particular advantage of the described invention is that the caller does not need to add a special prefix or suffix to the telephone number of the call recipient in order to initiate a reverse charge call, as the network provides the necessary functionality and leaves the choice of whether or not to initiate a reverse charge call to the call recipient. The call recipient will typically choose to accept the call charges (or a part thereof) from callers forming part of a known group, such as family members, or from other known callers, whose numbers and names will typically be in the phone book of the call recipient's mobile phone (or at least will be recognised by the call recipient).

Finally, although the invention has been described with reference to the use of mobile telephones, it will be appreciated that the described method and system can be operated with conventional telephones (particularly those providing a"caller ID"function), and other terminals such as computers with modems usable to make calls via a telephone network.